The present invention relates to a fixing device that uses induction heating to fix an image on a print medium in an image forming apparatus such as an electrostatic copying machine, printer, or the like.
A fixing device used in an image forming apparatus fixes a developing agent such as toner on a print medium by melting a toner layer formed on the surface of the print medium by heating. A fixing device which is related to the present invention uses a halogen lamp or the like as a heating source. The lamp is arranged inside a heat roller to heat it. A press roller is pressed against the heat roller and rotated so as to bring the print medium into press contact with the heat roller, and a paper sheet is passed between the two rollers.
FIG. 26 shows a schematic structure of the overall fixing device. A halogen lamp 102 is arranged inside a thin, metal heat roller 101. An elastic member is formed on the surface of a press roller 103 to make the print medium in sufficient press contact with the heat roller 101. The heat roller 101 and press roller 103 are supported while being applied with a predetermined pressure by a compression mechanism (not shown). Furthermore, the heat roller 101 and press roller 103 are rotated by a drive source (not shown) in the directions of arrows at the same speed as the convey speed of the print medium.
In the fixing device using the halogen lamp 102, light and heat coming from the halogen lamp in the heat roller are radiated in all directions to heat the entire roller. For this reason, losses occur upon converting light into heat, and upon warming up air in the heat roller and conducting heat to the heat roller. Therefore, the overall heat conversion efficiency is as low as 60 to 70%, resulting in poor power economy. Also, a long warm-up time is required from when the power supply is turned on until the heat roller 101 reaches the temperature required for fixing operation.
It is, therefore, an object of the present invention to provide an induction heating fixing device which has high heat efficiency, can attain power savings, and can shorten the warm-up time from power ON until the beginning of fixing operation.
According to the present invention, there is provided an induction heating fixing device comprising a hollow heat roller, a surface of which has a coat of a metal layer, induction heating means, arranged in the heat roller, for generating a magnetic flux in the heat roller to heat the heat roller by induction, and a press roller which is in contact with the heat roller under a predetermined pressure, wherein the induction heating means has at least two maximal heating portions in a circumferential direction of the heat roller, and the induction heating means is located to form at least one of the maximal heating portions within a range of xc2x130xc2x0 along the circumferential direction from a position of a nip where the heat roller contacts the press roller.
The device may further comprise a temperature sensor for detecting a temperature of the heat roller, and the temperature sensor may be located to fall within a range of xc2x130xc2x0 along the circumferential direction from the position of at least one of the maximal heating portions.
The device may further comprise a release agent applying roller for applying a release agent onto an outer circumferential surface of the heat roller, the induction heating means may have at least one minimal heating portion in the circumferential direction of the heat roller, and the release agent applying roller may be located to fall within a range of xc2x130xc2x0 along the circumferential direction from a position of the minimal heating portion.
An induction heating fixing device for an electrophotography apparatus of the present invention comprises a hollow heat roller, a surface of which has a coat of a metal layer, induction heating means, arranged in the heat roller, for generating a magnetic flux in the heat roller to heat the heat roller by induction, and a press roller which is in contact with the heat roller under a predetermined pressure, wherein the heat roller includes, as the metal layer, at least a first metal layer having first thermal conductivity, and a second metal layer having second thermal conductivity higher than the first thermal conductivity, and a thickness of the first metal layer in a radial direction of the heat roller is larger at end portions of the heat roller in a longitudinal direction than at a central portion in the longitudinal direction.
The thickness of the second metal layer in the radial direction of the heat roller may be constant from two end portions of the heat roller in the longitudinal direction to the central portion thereof in the longitudinal direction.
The thickness of the second metal layer in the radial direction of the heat roller may be larger at end portions of of the heat roller in the longitudinal direction than at the central portion thereof in the longitudinal direction.
A total thickness of the first and second metal layers in the radial direction of the heat roller may be constant over the longitudinal direction of the heat roller.
The device may further comprise a drive mechanism for rotating the heat roller, and the drive mechanism may drive the heat roller to vary a stop position with respect to the maximal heating portions of the induction heating means every time the heat roller is stopped.
An induction heating fixing device for an electrophotography apparatus of the present invention comprises a hollow heat roller, a surface of which has a coat of a metal layer, induction heating means, which is arranged in the heat roller and has an excitation coil, for generating a magnetic flux in the heat roller by supplying a current to the excitation coil to heat the heat roller by induction, and a press roller which is in contact with the heat roller under a predetermined pressure, wherein an insulating sheet is inserted between an inner surface of the heat roller and the excitation coil, and the insulating sheet has magnetic flux shielding portions for shielding the magnetic flux generated by the excitation coil for two end portion regions of the heat roller in a longitudinal direction.
The device may further comprise a rotation mechanism for rotating the excitation coil relative to the insulating sheet, and the rotation mechanism may rotate the excitation coil to locate the magnetic flux shielding portions in the vicinity of portions where a density of magnetic flux generated by the excitation coil has a first value, when a print medium having a first width undergoes a fixing process, and to locate the magnetic flux shielding portions in the vicinity of portions where the density of magnetic flux generated by the excitation coil has a second value higher than the first value, when a print medium having a second width smaller than the first width undergoes the fixing process.
In this case, when a temperature sensor is equipped, the temperature sensor is preferably located at a position which has aphase angle xcex1 with respect to aposition of one of maximal heating portions along the circumferential direction, and in which xcex1 is substantially equal to xcex2/2 where xcex2 is the maximum rotation angle of the excitation coil.